U.S. patent number 4,561,738 [Application Number 06/436,876] was granted by the patent office on 1985-12-31 for field tester.
This patent grant is currently assigned to Humphrey Instruments, Inc.. Invention is credited to Charles Campbell, William E. Humphrey.
United States Patent |
4,561,738 |
Humphrey , et al. |
December 31, 1985 |
Field tester
Abstract
A field tester wherein a patient's tested eye is located at the
center of an interior hemisphere defining a projection surface and
wherein a light spot is projected onto said surface from an
eccentric location is disclosed. Optics in common with the
projector assure that the off-center projected light is of constant
intensity and diameter as selected for each test sequence according
to test criteria. Specifically, a filament light source is
projected to a collimating lens. The light source is re-imaged to a
system lens stop. There is a movable aperture between the
collimating lens and the first lens of telescopic optics for
projecting the image of the aperture onto the projection surface of
the sphere. By using a coordinate transform to predict the distance
from the point of light source projection to the projection surface
of the sphere, the movable aperture is registered to a conjugate
distance with respect to the telescope optics. Aperture
registration insures projection of a constant image of the aperture
to any point along sphere surface. There results a field testing
spot of constant diameter and intensity, according to selected
image criteria, in spite of a continuously changing distance
between the point of projection and projecting surface on the
inside projection hemisphere. An apertured finder for centering of
the patient's eye is also disclosed wherein relay optics projecting
a real image of the patient's eye as viewed through a peep hole
assure a wide angle view of the eye being tested. The eye is viewed
through an aperture having a sight that does not significantly
interfere with the test being conducted.
Inventors: |
Humphrey; William E. (San
Leandro, CA), Campbell; Charles (Berkeley, CA) |
Assignee: |
Humphrey Instruments, Inc. (San
Leandro, CA)
|
Family
ID: |
23734181 |
Appl.
No.: |
06/436,876 |
Filed: |
October 26, 1982 |
Current U.S.
Class: |
351/226 |
Current CPC
Class: |
A61B
3/024 (20130101) |
Current International
Class: |
A61B
3/024 (20060101); A61B 3/02 (20060101); A61B
003/02 () |
Field of
Search: |
;351/224,225,226 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
E L. Greve, R. W. De Boer and H. Pynappel-Groothuyse, Perimetron,
Docum. Ophthal. Proc. Series, vol. 22, p. 69. .
E. L. Greve, Peritest, Docum. Ophthal. Proc. Series, vol. 22, pp.
71-73..
|
Primary Examiner: Bovernick; Rodney B.
Attorney, Agent or Firm: Townsend and Townsend
Claims
We claim:
1. An off-center projection system for a hemispheric projection
surface, comprising:
a light source;
means for collimating light from said light source;
a movable apertured member within a path of said collimated
light;
telescopic optics within said collimated light path for projecting
an image of said aperture onto said projection surface; and
means for moving said apertured member wherein said projected image
size and intensity remains constant, according to selected image
criteria, despite a constantly changing distance between a point of
projection and a point on said projection surface where said image
is formed.
2. The projection system of claim 1, said telescopic optics further
comprising:
a first mirror pivotable about a first axis for projecting said
image onto said projection surface; and
means for pivoting said mirror.
3. The projection system of claim 2, said telescopic optics further
comprising:
a second mirror about a second axis, orthogonal to said first
mirror pivot axis for projecting said image onto said projection
surface; and
means for pivoting said second mirror.
4. The projection system of claim 3, said collimating means further
comprising:
a first condensing lens proximate to said light source and located
on one side of said apertured member.
5. The projection system of claim 4, further comprising:
an optical stop along said light path.
6. A field tester, including an off-center projection system for
forming an image having constant size and brightness over varying
distances, according to selected image criteria, onto a hemispheric
projection surface, comprising:
a light source;
a condenser collimator for supplying constant light energy from
said light source over a collimated light path;
an apertured member movable along and within said collimated light
path, said member receiving light of substantially constant
intensity from said collimator;
means for moving said apertured member selected distances to and
from said light source along said light path; and
a constant magnification telescope within said collimated light
path including an optical train for projecting an image of said
member's aperture onto said projection surface, said optical train
including at least a first lens at an image reception point and a
second lens at an image projection point.
7. The field tester of claim 6, said apertured member further
comprising:
a plurality of individually selectable apertures having differing
diameters.
8. The field tester of claim 6, further comprising:
a neutral density filter having a selectively variable density and
interposed within said optical train.
9. The field tester of claim 6, further comprising:
a color filter wheel having selectable filter elements of varying
colors and interposed within said optical train.
10. The field tester of claim 6, further comprising:
light detecting means for receiving light from said hemispheric
projection surface, said light being indicative of intensity on
said projection surface and indicative of intensity of said
projected image, said light detecting means including means for
effecting changes in said image intensity to maintain a constant
image intensity during a test sequence.
11. The field tester of claim 6, further comprising:
a first mirror, within said telescope and pivotable about a first
axis, for folding said optical train;
a second mirror, within said telescope and pivotable about a second
axis, orthogonal to said first mirror pivot axis, for projecting
said image through said second lens and onto said projection
surface; and
means for pivoting said first and second mirror wherein said
telescopic optics may project an image onto said projection surface
at any selected location thereon.
12. The field tester of claim 11, further comprising:
an optical stop within said optical train.
13. The field tester of claim 11, further comprising:
servo means, coupled to said movable apertured member and to said
first and second pivotal mirrors, for maintaining conjugate
distance of said member's aperture from said telescope optics first
lens as a function of distance from said point of projection to
said projection surface.
14. The field tester of claim 13, said servo means further
comprising:
first stepper motor means for moving said apertured member along
said light path to and from said first telescope lens;
second stepper motor means for pivoting said first mirror about
said first axis;
third stepper motor means for pivoting said second mirror about
said second axis; and
each stepper motor including edge detector means for sensing the
position of each stepper motor relative to an initial motor
position.
15. Apparatus for testing field of vision of a patient's eye
comprising:
a hemispheric projection surface including a peep hole formed
through a center portion thereof;
a source of collimated light;
telescopic optics within a path of said collimated light for
projecting a test image onto said projection surface from a point
of projection off-center of said projection surface;
a movable apertured member within said collimated light path, said
member interposed between said light source and said telescopic
optics to form a test image of said aperture for projection by said
telescopic optics;
means for moving said apertured member wherein said projected test
image size and intensity remain constant according to selected
image criteria although there is a varying distance between the
point of projection and each point on said projection surface where
said test image is formed;
a first lens, positioned at a fixed distance from said peep hole on
a convex side of said hemispheric projection surface, for forming
an image of said peep hole onto an examiner's eye; and
a second lens, positioned a fixed distance from said first lens,
for viewing said peep hole image to center the patient's eye.
16. A field tester, comprising:
an off-center projection system for forming an image having
constant size and brightness according to selected image criteria,
over varying distances onto a hemispheric projection surface,
including:
(a) a light source;
(b) a condenser collimator for supplying constant light energy from
said light source over a collimated light path;
(c) an apertured disc, movable along and within said collimated
light path, said disc receiving light of substantially constant
intensity from said condenser collimator;
(d) means for moving said apertured disc selected distances to and
from said light source along said light path; and
(e) a constant magnification telescope within said collimated light
path, including an optical train projecting an image of said disc's
aperture onto said projection surface, said optical train including
a first lens located at an image reception point and a second lens
located at an image projection point; and
a wide angle viewing system for centering a patient's eye during
field of vision testing, including:
(a) a peep hole formed through a center portion of said hemispheric
projection surface;
(b) a first lens positioned at a fixed distance from said peep hole
on a convex side of said hemispheric surface for forming an image
of said peep hole onto an examiner's eye; and
(c) a second lens positioned a fixed distance from said first lens
for viewing said peep hole image.
17. A method for forming an image having constant size and and
brightness according to selected image criteria over varying
distances onto a hemispheric projection surface of a field tester,
comprising:
collimating a source of light to supply constant light energy from
said light source over a collimated light path;
forming an image to be projected on said hemispheric projection
surface with a movable apertured member;
projecting said image onto said projection surface with a constant
magnification telescope; and
maintaining said projected image at a constant size and intensity
according to selected image criteria on said projection surface by
moving said apertured member to and from said constant
magnification telescope in response to change in distance from a
telescope point of projection to said hemispheric projection
surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to field testers. More specifically, this
invention includes a field tester of type wherein the inside
surface of a projection hemisphere provides for visual field
intensity testing with a movable spot of light having examiner
selected parameters, such as size, intensity, and brightness, that
are maintained constant during a testing sequence in spite of
continuously changing focal length and distance from an image
projection point.
2. Description of the Prior Art
Field testers are known. It is common to include a hemispheric
projection surface and place the tested eye of the patient at the
center of the hemisphere. Thereafter, light sources are
sequentially flashed on the surface of the hemisphere. After
instructing the patient to a central fixation, an examiner notes
the ability of the patient to see the sides of the sphere and the
light sources flashed. The patient's so called "field" is
thereafter recorded and used to plot the absence, presence, and
even progress of disease.
These instruments are of several types. In a first type, an array
of lights is mounted to penetrate through the surface of the sphere
(see for example Gains, U.S. Pat. No. 3,288,546). Such devices are
usually limited in the color and intensity of light projected as by
the type of light source used. For example, where diodes are used,
only monochromatic tests are possible.
In another type of device, light projection is made to coincide as
closely as possible to the center of the sphere where the patient's
eye and forehead frequently reside. As a consequence, the point of
beam projection physically interferes with the point of patient
placement. Thus, all the difficulties of off-axis projection are
present, including improper focus of a light beam on the inside
projection of the dome and variation in intensity of the projected
light beam. (See for example Krahn U.S. Pat. No. 4,045,130).
Off-center projection has heretofore been used. Such projection has
included scanning the inside surface of the hemisphere with a
target path comprising a plurality of semi-closed loops. Generally,
the path of the loops has been directed to all points on the inside
surface that are equidistant from a projection point. The image is
projected in a great circle fashion such that sectors of the inside
surface are defined. When one sector has been tested, the projector
is moved and another sector is tested. The projector is typically
moved in one of two ways: it is swung by a mechanical arm
horizontally and transverse of the inside surface in an arc, or it
is moved about the periphery of the inside surface. These
approaches, although maintaining constant image size and intensity
due to the equal distance from the projection point to the inside
surface for all points in a sector, are not ideal in a testing
environment. The device of the type having a mechanical arm is not
suited for automated testing; the arm must swing behind the
patient's head during the test, creating a hazard wherein the
patient could bump into the swinging area. The device having
peripheral projection requires complex rotary movement of its
entire optical system. Such an approach unnecessarily complicates
the field tester mechanism.
SUMMARY OF THE INVENTION
A field tester wherein a patient's tested eye is located at the
center of an interior hemisphere defining a projection surface and
wherein a light spot is projected onto said surface from an
eccentric location is disclosed. Optics in common with the
projector assure that the off-center projected light is maintained
at constant intensity and diameter, as determined by examiner
selected parameters. Specifically, a filament light source is
projected through a collimating lens. The light source is re-imaged
to a system lens stop. There is a movable aperture between the
collimating lens and telescopic optics for projecting the image of
the aperture onto the projection surface of the sphere.
By using a coordinate transform to predict the distance from the
point of light source projection to the projection surface of the
sphere, the movable aperture is registered to a conjugate distance
with respect to the telescope optics. Aperture registration insures
projection of a constant image of the aperture to any point along
the sphere surface. There results a field testing spot that is
maintained at constant diameter and intensity, according to
examiner selected criteria, in spite of a continuously changing
distance between the point of projection and the projection
surface.
An apertured finder for centering of the patient's eye is also
disclosed wherein relay optics projecting a real image of the eye
assure a wide angle view of the eye being tested. The eye is viewed
through an aperture having a sight that does not significantly
interfere with the test being conducted.
An object of the invention is to disclose an off-center projection
system for a hemispheric projection surface which projection system
preserves projected image size and image intensity, as selected
according to examiner specified test criteria, in spite of
constantly changing distance between the point of projection and
the point on the inside surface of the hemisphere where projection
occurs. According to this aspect of the invention, a light source
is projected through a collimator to the first lens of telescopic
optics for projecting an image to the inside and projection surface
of the projection hemisphere. An aperture is movable along the path
of collimation where it can only receive light of substantially
constant intensity even though it is moved varying distances from
the light source. By the expedient of moving the aperture to a
conjugate distance with respect to the telescopic optics,
projection of an image of the aperture to the inside surface of the
hemisphere is assured. At the same time, the intensity of the image
on the inside surface of the hemisphere remains unchanged, even
though the projection distance constantly changes.
An advantage of the disclosed lens train is that it may be
conveniently folded by moving mirrors. For example, by a system of
two orthogonal pivoted mirrors, the beam may be projected to all
surfaces on the inside of the projection hemisphere.
Another advantage of the present invention is that the size of the
projected spot remains the same. Specifically, it is a property of
the disclosed telescope that as the aperture moves towards the
first lens of the telescope, the resultant beam is focused for
projection at a further distance. However, the end and resulting
size of the spot remains constant.
It is a surprising result of this invention that the projection of
the spot varies in projected distance without changing in
intensity. According to this aspect of the invention the aperture
movable in the collimated light path must by definition always emit
the same amount of light. This is true whether the aperture is
towards the light source or away from the light source. Since the
remaining telescopic optics serve only to relay the image to the
conjugate location, the image uses only that light passed by the
aperture, the light passed by the aperture being constant because
of collimation.
An advantage of the disclosed lens train and constant image
projection system is that a white full spectrum source can be used
for projection. Moreover, the interposition of neutral density
filters and color filters allow for testing of the eye throughout
the observable spectrum.
Yet another object of this invention is to disclose a wide angle
viewing system for centering of the eye of the patient to be tested
in the center of the sphere. According to this aspect of the
invention, an insignificant and small hole in the nature of a "peep
hole" is placed in the back of the observing hemisphere. A lens is
placed behind the hemisphere with the peep hole at a first
conjugate location and the eye of the observer at a second
conjugate location. A suitable eyepiece is used for viewing the
real and projected image of the patient's eye a short distance away
from the eye of the observer. There results a wide angle view of
the patient's eye being tested in the field tester, which wide
angle enables rapid and precise centering.
An advantage of this aspect of the invention is that the
interference of the hole with the projection surface on the inside
of the hemisphere is insignificant. Additionally, light source
projection to the center of the hemisphere along the patient's line
of sight can easily be made.
Yet another aspect of this invention is that the peep hole used for
eye centering can also be used for a light fixation source of a
patient. This light fixation source can either be combined with the
centering optical train or alternately can be a small and
independent source.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features, and advantages of this invention will
become more apparent after referring to the specification, and
figures, in which:
FIG. 1 is an over all perspective view of the invention shown from
behind and above a patient and illustrating the placement of the
patient's right eye at the center of the projection sphere, the
off-center projection of the field spot, and the eye only of the
examiner in suitable position for observing and centering the eye
of the patient within the instrument;
FIG. 2 is an optical schematic shown in three dimensions
illustrating the projection of a light beam in substantially the
same position as the projection illustrated in FIG. 1;
FIG. 3 is a second schematic of the light projection source of FIG.
2 illustrating the projection of light to a second and greater
distance from the projection source and illustrating the movement
of the projecting mirror and aperture to assure a focused image of
constant intensity at a different distance from the light source;
and
FIG. 4 is a schematic of the light centering optics of this
invention illustrating the projection of the eye of the examiner to
and towards the peep hole;
FIGS. 5a-5j show a coordinate system wherein a mathematical model
of the present invention is described; and
FIGS. 6a-6c show a coordinate system wherein a mathematical model
of a stepper motor and bell crank portion of the present invention
are described.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
The present invention is a field tester 10 (FIG. 1). In the Fig., a
patient 11 is seated on a stool 14 in front of the field tester
cabinet 16. The patient rests his chin on a chin rest 19 supported
by a patient positioning frame 18. The patient's eyes 12 are
aligned through a viewing system 23 by an examiner 13. The patient
gazes into the center portion of a hemisphere 20 which includes a
projection surface 21. A series of images are formed upon the
hemispheric projection surface 21 by a projection system 22.
The purpose of the field tester is to test the patient's field of
vision. To this end, a spot of light (the image) is projected at
different locations onto the hemispheric surface. If the patient is
able to see the projected image, he so indicates it to the
examiner. The examiner notes the location of those images seen by
the patient and thus can create a field of vision map. The field of
vision test results may also be determined by a calculating device
(not shown).
The projection system 22 in the present invention provides
off-center projection of an image onto the hemispheric surface 21
while maintaining constant light intensity and spot (image) size
during the test, in accordance with the test parameters chosen by
the examiner. The off-center arrangement of the projection system
prevents interference by the projection system with the location of
the patient's head within the field tester. It is essential that
the projected image be maintained at its selected size and
brillance during each test sequence such that an accurate
measurement of the patient's field of vision is obtained. For
example, an image of varying intensity or size may or may not
elicit a response from the patient when a particular portion of the
field of vision is being tested. Such a result may not have been
obtained had the image been of a constant size or intensity. Thus,
an error is produced, making the diagnosing of progressive diseases
of the eye much more difficult.
The projection system 22 comprises a light source 26 (FIG. 2) for
illuminating the image to be formed. The light source may be any
light source such as a halogen incandescent lamp, as manufactured
by General Electric Company of Syracuse, N.Y.
Light emanating from the light source 26 is collimated by condenser
element 28. The collimated light behaves in such a manner that the
light rays are in parallel alignment and the light striking an
object is always of constant intensity.
Within the optical path or axis between condenser element 28 and
lens 29 is an aperture member such as disc 44 that includes a
plurality of various sized apertures 45a-45e. Light striking the
aperture disc 44 passes through an aperture near the optical axis
(aperture 45a in the example of FIG. 2). The light passing through
the aperture thereafter may be used to project an image of a light
dot onto the hemispheric projection surface.
The light passing through aperture 45a is intercepted by a shutter
58. The shutter allows light to pass during a testing interval and
prevents the passage of light during relocation of the image, prior
to or at the conclusion of a test.
After being passed by the shutter, light may be passed through a
filter wheel 50 including filters of various colors 54a-54f. By
selecting appropriate filters, the response of a patient's eye to
various light wavelengths may be determined. After passing through
the filter wheel, light passes through lens 29.
Lens 29 is the first lens in a constant magnification telescope
system for projecting the image onto the hemispheric surface. The
image striking lens 29 is focused at a focal point within an
optical train including lens 29, mirrors 34-36, and lens 30.
Interposed within the optical train is a variable neutral density
filter 51 for varying the intensity of light that passes through
the optical train. Additionally, there is an optical stop 32 in the
optical train for preventing interference due to reflection and
spurious images. The stop is smaller in size than light source
filament 26a so that movement of the filament does not result in
variation in light density within the image projected onto the
projection surface.
The optical train is folded by means of mirrors 34-36. The image
may be projected on any part of the hemisphere 20 projection
surface 21 depending on the positioning of mirrors 35 and 36.
Referring now to FIG. 3, a system of servos and detectors is shown.
Apertured disc 44 is shown having a slot 60 which is positioned
proximate to an edge detector 70. The edge detector indicates the
presence of the wheel slot and thus serves as an initialization
position for disc 44. The edge detector 70 produces a signal which
is provided to a drive (not shown) by which disc 44 may be rotated
about an axis as shown at 47. Rotation of the apertured disc allows
the examiner to position a selected aperture 45a-45e within the
light path in between light source 26 and the above-mentioned
optical train. In this way, images of various selected sizes may be
projected onto the hemispheric projection surface in accordance
with the requirements of each patient being tested.
The aperture disc assembly 44 has an additional edge detector 68
that senses the presence of the disc along the linear path between
the light source and collimator 28, and lens 29. Movement along
this path is indicated by line 46 in FIG. 3. Motion of the disc
along this path is accomplished by a drive, such as stepper motor
73 and associated linkage 101. It will be appreciated that although
edge detectors and stepper motors are shown, positioning of the
apertured objective can be just as readily accomplished by
mechanical (as opposed to electromechanical) means or it could be
manually positioned.
The projection system, which includes the telescopic optics 29/30,
allows an image to be formed at any position along the hemispheric
surface 21. To this end, a linkage arm 62 is connected to a linear
stepper motor 93, which is provided for rotating the projection
path (lens 30) from the optic train about a first axis as indicated
by 41. A drive means 64, comprising stepper motor 67, belt 66, and
pulley 65, is provided for rotating the projection path of the
optic train about a second axis, as indicated by 40.
Shutter 58 may be operated by conventional drive means (not shown).
Additionally, filter wheel 50 and neutral density filter 51 may be
rotated as indicated by 52 and 53, respectively. Such rotation
allows selection of varying color filters 54a-54f and varying
degrees of optical density. Rotation of the filter wheel and
neutral density filter is accomplished by a motor or other such
drive means (not shown). Additionally, neutral density filter 51
includes slot 49 and an associated edge detector 72 for sensing
filter positioning; filter wheel 50 position is also tracked by an
edge detector 102.
In one embodiment of the invention the neutral density filter may
be coupled to a photocell 63 and associated lens 63a. The photocell
monitors the background intensity of the projection surface 21 as
well as the intensity of the projected image itself. Background
intensity may be that of the ambient or a background light source
may be provided.
The photocell, in conjunction with the neutral density filter 51
and edge detector 72, may act as a light intensity fine tuning
servo. In other embodiments of the invention, the photocell
operates a light source brightness control (not shown).
In operation, the size of the projected image and intensity of the
projected image are maintained as a constant. As the image is
projected to different points on the hemispheric surface 21,
mirrors 35/36 are rotated about two axes 40/41. The mirrors are
mounted to a projection base, such as bell crank assembly 69 and as
such, the relationship between the mirrors is predictable.
FIG. 2 shows projection of an image 21 to point P1 on hemispheric
surface 21. To effect such projection, the angle of light reflected
from mirror 35 (A.sub.3) to mirror 36 and from mirror 36 through
lens 30 (A.sub.4) onto surface 21 is adjusted by positioning of the
mirrors about axes 40 and 41 respectively. Because the distance
from the point of projection at lens 30 to the hemispheric surface
21 varies from point P1 to P2 (FIG. 3), the size and intensity of
the image formed on a hemispheric surface would normally vary as
focus of the image changes with distance. Such variation in
intensity and image size tends to invalidate the results of the
field test, the accuracy and validity of each test sequence being
related to the use of a constant light source of fixed size. The
present invention solves the problem of variation of intensity and
image size by providing for lateral movement along the optical path
of the image forming apertured disc 44. As can be seen in FIGS. 2
and 3, the positioning of the disc is a function of the distance of
the projection surface from the point of projection.
Image intensity is maintained as a constant by the use of the
collimator 28 which provides a constant amount of light energy to
the apertured disc 44 and through the aperture (45a in the
exemplary embodiment) without regard to the positioning of the disc
and aperture along the optical path.
Constant image size and sharp image focus are maintained by moving
the image forming aperture 45a toward and away from the telescopic
optical train (lenses 29/30). The tendency of a projection system
using a fixed image is to provide a larger, out-of-focus projected
image at greater distances. To overcome this tendency, the position
of the projection surface, which is related to mirror positioning,
serves to control the positioning of the apertured disc to and from
the first lens 29 of telescopic optic. Thus, when the image is to
be formed at a greater distance, the apertured disc is accordingly
moved toward the first lens 29 of the telescopic optic, thereby
maintaining image focus and size as projected by the telescope.
To maintain accuracy of interaction of the mirror positions and the
positioning of the apertured disc, edge detectors (not shown) are
added to the mirror positioning stepper motors to locate mirror
position. Mirror positioning information is coordinated with
apertured disc location information as developed by edge detector
68. A mathematical model for positioning the mirrors and the
apertured objective, and a practical application of same are
provided in the following paragraphs.
Positions on the hemisphere are given by two numbers, .phi. and
.theta., as shown in FIG. 5a. FIG. 5b is a geometrical picture of
the hemispheric surface. It is equivlent to a left handed
coordinate system. It is also equivalent to a normal coordinate
system where all values of .theta. are negative numbers as shown in
FIG. 5c.
The most convenient system for describing image projector motion is
one in which the z axis is not in the patient's line of sight but
is coincident with the axis of rotation of the projection tower or
bell crank 69 (FIG. 5d). It follows that there is a rotation of the
coordinate system about the x axis. The position of an image in the
new system expressed in terms of its position in the old system is
given by the following transformation equation: ##EQU1## x, y, z
are taken to normalized coordinates such that x.sup.2 +y.sup.2
+z.sup.2 =1. From this is can be seen that x, y and z are expressed
in terms of .theta. and .phi. as follows:
Applying the above transformation:
From the equations:
it can be seen that .phi.=cos.sup.-1 z and .theta.=tan.sup.-1 y/x.
The .phi. and .theta. values in the new system are: ##EQU2##
The geometry of the projector head is shown in FIG. 5e. For
purposes of the example:
The light path is from (1) to (2) to (3) and to the image formed on
the hemisphere at location .phi.', .theta.'. A method is needed to
calculate rotation of the projector elements, .phi." and .theta.",
when .phi.' and .theta.' are known. It can be seen from FIG. 5f
that once .phi." is given a fixed value, the value of .phi.' is
also fixed no matter what value of .theta." is chosen. That is,
if:
then:
However light travels on a dog leg path (FIG. 5g). To know path
length, the value of p(.phi.') must be known. Once r(.phi.') is
known it can be seen that:
Therefore, if:
then:
Now it is necessary to calculate .phi." from a given value of
.phi.'. .gamma. is defined as shown in FIG. 5h so that:
Referring to FIG. 5i, a line, z", parallel to z' is drawn through
point (3). The angle between z" and the line from (3) to the
projected spot (5) is .phi.". The length of the line,
(3).fwdarw.(4), is p(.phi.') cos .phi.". The length of the line,
(2).fwdarw.(5), is r(.phi.') cos .gamma.'. Because (3).fwdarw.(4),
and (2).fwdarw.(5) are parallel and are projected from the same
spot, they are of equal length. Therefore:
Since p(.phi.'); R, cos .phi.' and "a" are known, .phi." is given
by: ##EQU3## where: cos .phi.'=z'=cos .phi. cos (72.5.degree.)+sin
(72.5.degree.) sin .phi. sin .theta..
The calculation of .theta." is described next. For any fixed value
of .phi.', the value of .theta." is an angular displacement from
some reference or starting position of the tower, picked so that
the reference position coincides with the .theta.=0.degree.
meridian. However, as .phi.' changes, the reference position also
changes. This change must be accounted for in the calculations. To
start, a reference position .theta..sub.o " for the case
.theta.=0.degree., .phi.=0.degree. is defined. The reference is
given by describing the direction of line (2).fwdarw.(3) in .phi.',
.theta.' space. When .phi.=0.degree.=.theta., x'=0, y'=-sin
.delta., and z'=cos .delta.. Therefore, ##EQU4##
In FIG. 5j, point (5) on axis z' is placed so that angle <z'(5)S
is a right angle. As discussed above, line (3).fwdarw.(4) is
parallel to line (2).fwdarw.(5). Since angle <(2)(3)(5) is a
right angle and line (5).fwdarw.(4) is parallel to line
(2).fwdarw.(3), angle <(5)(4)(5) is also a right angle. The
length of line (2).fwdarw.(3) is known to be, b. Therefore, line
(5).fwdarw.(4) is also length, b. Because of this construction,
line (5).fwdarw.(S) is length R sin .phi.'. Thus, R sin .phi.' cos
.theta..sub.o "=b, where .theta..sub.o " is angle <S(5)(4), the
direction of line (5).fwdarw.(4) and the direction of line
(2).fwdarw.(3). Therefore: ##EQU5##
For any other value of .theta.', .theta." is defined by:
##EQU6##
Rotation about the .phi." axis is accomplished by a linear stepper
motor 93 and associated linkage 62 driving a bell crank 69 which
rotates about the .phi." axis. As FIG. 6a shows,
Since d.sup.2 =c.sup.2 +e.sup.2 ; then cd=c(c.sup.2
+e.sup.2).sup.1/2. Referring to FIG. 6b, there is used as a
reference the position for which .gamma.=90.degree.. m and c can be
directly measured when .gamma.=90.degree. and used to compute
.beta..sub.o where .beta..sub.o =tan.sup.-1 m.sub.o /c.
The position for which .gamma.=90.degree. is the midtravel position
for the .phi." stepper motor. It corresponds, by design, to a value
of .phi.'. However, .phi.' can also be measured on the hemisphere,
which is the best way to proceed. Knowing .phi.', the next
calculation is .phi.", where ##EQU7## As can be seen in FIG. 6c,
.beta.+.alpha.+.phi."-.phi..sub.o "=180.degree.,
.beta.+.phi."=180.degree.-.alpha.+.phi..sub.o ".
Since .alpha. and .phi..sub.o " are constants, the sum
.beta.+.phi." is also a constant. This means that any change in
.beta. results in an equal change in magnitude in .phi." and
vice-versa. The signs of the changes are opposite. .phi..sub.o "
can be set at any value as long as it is a constant. .phi..sub.o "
is re-chosen as that value, which represents the value of .phi." at
.gamma.=90.degree.. Also .beta..sub.o is defined as the value of
.beta. when .gamma.=90.degree.. Then .beta.=.beta..sub.o
+.DELTA..beta.. But .DELTA..sup..upsilon. .beta.=-.DELTA..phi."
when .DELTA..phi."=.phi."-.phi..sub.o ". So .beta.=.beta..sub.o
+.phi..sub.o "-.phi.". Describing m as a function of .beta.:
S.sub..phi. " is the number of motor steps off the zero or initial
position, L is the motor inches/step, m.sub.o is the value of m at
the initial position. ##EQU8##
For the .theta." drive, the tower is belt driven by drive system 64
with a reduction of N. Therefore, since the reference position is
taken as .theta."=0, ##EQU9##
There is also aperture motor drive 73 to consider. Its function is
to keep the image of the aperture on the hemispheric surface in
focus. For purpose of illustration, the telescopic lens system 29,
30 will be taken to have telescopic power 2, although other powers
would be workable. Then the optical system is such that a change of
.DELTA.x in aperture position results in a change of 4.DELTA.x in
the position of the aperture image. The image of the aperture is
measured from the objective lens 30. This lens is at a distance D
from the hemispheric surface where: D=.rho.(.phi.')=f, where f will
be taken as 1" in this example.
For some initial arrangement in which, D=the correct image
distance, a change of .DELTA.D must be accompanied by a change of
(.DELTA.D)/4 in the aperture position to maintain focus. If
.DELTA.D=D-D.sub.o, and if x.sub.o is the x position corresponding
to good focus at D.sub.o ; then, since ##EQU10## If the motor
rate=A(inches/step), then ##EQU11## If desired, it is possible to
alter the value of x.sub.o for a given D.sub.o by interposing an
additional lens 30a (shown in phantom) between lens 29 and lens 30.
Such additional lens would be a mechanical expedient, allowing the
travel path of the aperture disc to be shifted.
There are now developed the equations necessary to generate motor
commands once values of .theta. and .phi. are chosen. The
calculations are done most directly in the following order.
Representative constants are used for illustrative purposes but are
by no means the only values which can be used in practice.
##EQU12##
The edge detector and stepper motor type servo is well known in the
art. Basically, the edge detector defines a reference or initial
location for the servo component, such as the apertured disc. The
stepper motor moves a control component a predictable distance for
each drive pulse it receives. Thus, if three pulses of a first
polarity are supplied to the step motor when the controlled
component is at the edge detector, two things are known: the number
of pulses of opposite polarity required to return the component to
the edge detector position and the distance the component has been
moved from the edge detector.
In some embodiments of the invention, a photocell and lens 63 is
also added, as discussed above, for sampling background intensity
and projected image intensity. The photocell determines the Weber
fraction or contrast, and fine adjusts the intensity of the image,
if necessary, to maintain constant image intensity. The Weber
fraction is defined as follows:
where:
L=background luminance; and
.DELTA.L=L.sub.s -L.sub.b (luminance of source minus background
luminance).
To insure accurate field testing, the patient's eye must remain
constantly fixated on a reference location, such as a center
portion of the hemisphere 20. To maintain such alignment, it is
desirable to monitor the positioning of the patient's eye, as well
as to provide a fixation point for the patient. FIG. 1 shows a view
finding system 23 and an observer's eye 13. FIG. 4 shows the view
finding system 23 in detail. A peep hole 15 is provided at a center
portion of the hemisphere 20. The peep hole should be small and
should be positioned such that a patient's eye may easily be
aligned with it. Because the surface of the tester is maintained in
relative darkness to allow easy perception of the projected images
by the patient, very little light is reflected from the patient's
eye. Thus, a viewing and centering system must efficiently use the
available light.
The present invention comprises a mirror 76 which gathers light
passing through peep hole 15 and reflects said light to a first
lens 77. The positioning and refractive power of the first lens 77
is such that it creates, in conjunction with second lens 78, an
image of peep hole 15 in the plane of and centered in the pupil of
the examiner's eye 13. In addition, lens 77 and 78 create a
magnification system such that the image created of the peep hole
13 is the same size as or a little smaller than the pupil of the
examiners eye 13. Therefore, all the light passing through peep
hole 13 into first lens 77 passes into the examiner's eye with
little loss. Indeed, it is as though the examiner physically
pressed his eye against peep hole 13 and viewed the patient's
eye.
First lens 77 also creates a real image of the patient's eye in the
space between lens 77 and the second lens 78. Second lens 78 is
positioned so that this real image falls at approximately one focal
length from it. In addition reticle 79 is placed in the plane of
this real image so that both it and the real image can easily be
viewed simultaneously in focus by the examiner. Reticle 79 is
provided with cross hair 80 to aid in centering the patient's eye
and with a graduated scale by which the size of the patient's pupil
may be measured.
To fixate the patient's eye a first light source such as LED 82 is
provided. The LED 82 is centered on mirror 76 such that the patient
most clearly perceives the light source when his eye is in proper
alignment for field testing.
To add further precision to the fixation system a second light
source, such as LED 81, may be added at lens 77. Thus, two points
of fixation are provided such that when the eye is aligned, the
light sources 81/82 converge. Such a system assures a high degree
of accuracy when aligning a patient's eye for field testing. It
will be appreciated that other light sources, such as neon lights,
lamps, etc. may be used in place of the LED.
The present invention provides a field tester including a
off-center objection system that does not interfere with alignment
of a patient's eye within a hemispheric projection surface of said
field tester. By use of the above described optical train a
projected image, selected according to predetermined criteria, is
maintained in a constant size and intensity on the hemispheric
projection surface during a testing sequence. As a result,
excellent accuracy is obtained in field testing. To further enhance
the reliability and accuracy of tests performed with this device, a
wide angle viewing device has also been described for aligning the
patient's eye by observation or by patient fixation.
It will be appreciated that modifications and variations may be
made to the invention as described without departing from the scope
and spirit of the invention as claimed. For example, the optical
train may be further folded by the inclusion of additional mirrors,
positioning of the apertured disc and the mirrors may be
accomplished by servo systems other than those described above or
by manual adjustment, etc. Therefore, the scope of the invention
should be limited only by the breadth of the claims.
* * * * *